As the small loudspeaker mounted to the mobile telephones, lap-top personal computers and the like, such small dynamic loudspeaker having inner-magnet type magnetic circuit as shown in FIG. 6 has been widely employed. This small type loudspeaker is constituted by forming a magnetic gap with a yoke 14 and a plate 13, placing a magnet 15 on the yoke 14 and further the plate 13 made of a magnetic member thereon, and disposing a voice coil 12 coupled to a diaphragm 11 within the magnetic gap.
Now, the mobile telephones have been developed more and more in the multiplicity of types and functions, whereas still further minimization in the dimensions and weight has been demanded in view of the convenience of portability, and necessarily the small loudspeakers mounted thereto have been strongly demanded to be also small and ultra-thin.
Since such general dynamic loudspeaker as shown in FIG. 6 is of a driving system employing a single magnetic gap and a single voice coil, it becomes difficult to maintain required sound pressure level, frequency characteristics and so on as the dimensional and thickness minimization advances, and this type of the loudspeaker is limited in the possibility of response to the foregoing demands.
On the other hand, there has been known old such flat speaker of full-face driving as shown in FIG. 7 in its basic arrangement, in which a planar diaphragm 21 provided with a voice coil 22 is driven in the full face in equiphase with a plurality of magnets 25 disposed as dispersed on a plane board 23 having a plurality of holes 26, and which is featured in the capability of restraining occurrence of divided vibration and attaining flat frequency characteristics. However, this loudspeaker has been inferior in the conversion efficiency due to its structure, difficult to have both of a sufficient sound pressure and a wide band reproduction satisfied, almost limited in the usage to that as a tweeter, and unable to be used for the wide band. In manufacturing this type of the loudspeaker, further, it has been required to provide the diaphragm as glued in tense state, the planar diaphragm 21 has had to be fixed as adhered under a tension applied, and the workability has been extremely deteriorated.
In the small loudspeakers mounted to mobile telephones and the like, the conventional small loudspeaker of general dynamic type is unable to respond to the demand of minimization to be ultra-thin.
Since it is difficult to have both of the small and light-weight type as well as the sufficient sound pressure and wide band reproduction satisfied, the conventional flat speaker of full-face driving is not suitable for use as the small loudspeaker in the mobile telephone and lap-top personal computer.
The present invention has been suggested in view of such respects, and its object is to easily provide a flat speaker of full-face driving capable of realizing the sufficient sound pressure and wide-band reproduction even being the ultra-thin type, and responding to severe needs of the mobile telephone and the like.